Attributes don't get serialized - but why?

I have two applications sharing the same code base. One application is a web application (ASP.Net MVC3), which has some sort of API to accept JSON-Serialized data. The other application is a client-application that makes requests to the web application to
submit such data.

I am not very familiar with JSON.Net so there might be other ways to fix this; I noticed
JsonSerializerSettings which might be able to influence the serialization process but didn't find a setting there to get the desired output. Also implementing your own
JsonConverter (or
CustomCreationConverter<T>) looks promising for finer grained control on the (de)serialization process but is also more work.